package day04;

import java.util.Scanner;

public class txt13 {
    public static void main(String[] args) {
        Scanner s=new Scanner(System.in);
        int n=s.nextInt();
        int sum=0;
        for(int i=1;i<=n;i++){
            sum=sum+i;
        }
        System.out.println( sum);

    }
}
